Method for surface treating animal tissue

ABSTRACT

A method for surface treating animal tissue is provided by the invention. The method includes the steps of providing animal tissue having an average size of between about 0.5 inch and about 16 inches in length, introducing the animal tissue into a bath provided at a temperature of between about 80° C. and about 150° C. for between about 25 seconds and about 150 seconds, and recovering the animal tissue from the water bath. A pasteurization unit is provided for continuous processing of animal tissue.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for surfacetreating animal tissue. More particularly, the invention relates to theuse of hot water submersion techniques for reducing bacterialpopulations on the surface of animal tissue.

BACKGROUND OF THE INVENTION

There exists concern about pathogenic and enteric bacteria in animalmeat, and, in particular, ground beef. As a consequence of processinganimals into meat for human consumption, the surface of the animalcarcass may become contaminated with bacteria from many sourcesincluding processing equipment, workers, and the environment. Thepredominant source for bacterial contamination is the animal itself. Thehide, hooves, intestinal contents, and milk have the potential to harbornot only large numbers of bacteria but also pathogenic bacteria.Techniques have been utilized for reducing bacterial contamination ofthe animal carcass. For example, International Publication No. WO96/13983 describes an apparatus for steam pasteurization of the surfaceof meat carcasses. Other techniques for reducing the contamination ofthe carcass surface involves trimming defined areas on the carcass, andwashing the carcass with both hot and cold water. These techniques aredescribed by Phebus et al., “Comparison of Steamed Pasteurization andOther Methods for Reduction of Pathogens on Surfaces of FreshlySlaughtered Beef,” Journal of Food Protection, vol. 60, no. 5, 1997,pages 476-484. Techniques for treating buffalo meat cuts from shoulderand leg portion in hot water at 70° C. and 80° C. for 30 to 60 secondsis described by Sachindra et al., “Reduction in Microbial Load onBuffalo Meat By Hot Water Dip Treatment,” Meat Science, vol. 48, no.1/2, pages 149-157, 1998.

Bacterial populations have the opportunity to form on the exposedcarcass surface. A large percentage of the trimmings which are processedfor human consumption are obtained from this exposed carcass surface. Ithas been found that E. coli bacteria, and many pathogens, can reside onthe surface of carcass beginning with the carcass processing. Thepathogens can originate from fecal matter and other contaminants on thesurface of the meat. Without adequately destroying these pathogens, themeat is processed, and shipped to the distributor, retailer, orconsumer. It is then left for the consumer or preparer of the meat toaddress the problem that by then can be even worse. The bacteria mayhave further multiplied. Ground meats are very susceptible to bacteriagrowth because the surface pathogens can be distributed throughout themeat during processing.

SUMMARY OF THE INVENTION

A method for surface treating animal tissue is provided by the presentinvention. The method includes steps of: providing animal tissue havingan average size of between about 0.5 inch and about 16 inches in length;introducing the animal tissue into a fluid bath provided at atemperature of between about 80° C. and about 150° C. for between about25 seconds and about 50 seconds; and recovering the animal tissue fromthe water bath.

The animal tissue which can be processed by the method of the inventioncan include beef, poultry, swine, sheep, horse and wild game. The animaltissue can be introduced into the fluid bath immediately or shortlyafter the slaughter or fabrication operation, or after the animal tissuehas been cooled or chilled. In the case of animal tissue introducedshortly after the slaughter or fabrication operation, it is expectedthat the animal tissue will have a temperature of between about 30° C.and about 40° C. In the case of animal tissue which has been cooled orchilled, it is expected that the animal tissue will have a temperatureof between about 0° C. and 10° C.

The animal tissue is preferably advanced through the fluid bath in afirst in and first out arrangement. It should be appreciated that afirst in and first out arrangement reflects the situation where portionsof animal tissue do not remain or build up within the hot fluid bath.That is, tissue enters the hot fluid bath and then is removed after thedesired level of surface treatment. In order to provide a first in andfirst out arrangement, the animal tissue is preferably advanced orconveyed through the water bath using a rotation screw having a spiralflight extending from a first end to a second end for advancing theanimal tissue. Preferably, the rotation screw rotates at a rate of aboutone revolution per minute and about 20 revolutions per minute.

While the preferred heating media or bath is water, it should beappreciated that other types of heating media can be used includingtallow. When water is used as the heating medium, it is preferable toprovide the hot water at a temperature of between about 80° C. and 110°C., and to provide a surface treating period of between about 25 secondsand about 50 seconds. In the case of using tallow as a heating media, itmay be appropriate to increase the treatment time if the temperature ofthe heating media is maintained at between about 80° C. and about 110°C. Accordingly, at this temperature, it may be appropriate to surfacetreat the animal tissue for a period of between about 25 seconds andabout 150 seconds. Alternatively, the tallow can be provided at a highertemperature to provide a shorter treatment period. For example, thetallow can be provided at a temperature of between about 115° C. and150° C. in order to provide a treatment time which is between about 25seconds and 50 seconds. In addition, the size of the animal tissue canbe characterized in terms of weight. Preferably, the average weight of apiece of animal tissue is between about 0.25 lb. and about 12 lbs.

The invention relates to a method for preparing ground beef. The methodincludes the steps for surface treating animal tissue followed by a stepof processing the recovered animal tissue to provide ground beef.

A pasteurization unit is provided by the present invention. Thepasteurization unit includes a hot media containing trough, a rotationscrew, and a motor for driving the rotation screw. The hot mediacontaining trough has an animal tissue inlet at a first end, and ananimal tissue outlet at a second end. The hot media containing trough ispreferably constructed and arranged for holding hot media and animaltissue having an average size of between about 0.25 lb. and about 12lbs. per piece of animal tissue, and for providing surface treating ofthe animal tissue. By “hot media” it is meant that the temperature ofthe media is provided at a temperature which is sufficient to providelethal action on the bacterial populations which may be present on thepresent of the animal tissue during the time of surface treating theanimal tissue. In general, it is expected that the media will beprovided at a temperature of between about 80° C. and about 150° C.under most desirable periods for surface treating the animal tissue.Preferably, the media includes water, and may include fat or tallow. Therotation screw is provided having a spiral flight extending from thefirst end to the second end. The spiral flight is provided for advancingthe animal tissue from the first end to the second end. The motor isprovided for driving the rotation screw at a speed of between about oneand about 20 revolutions per minute. Preferably, the pasteurization unitincludes hot media inlet ports along a length of the hot watercontaining trough or introducing hot media into the hot media containingtrough.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of the method and apparatus for surfacetreating animal tissue according to principles of the present invention;

FIG. 2 is a top view of the pasteurization unit provided in FIG. 1; and

FIG. 3 is a side view of the pasteurization unit of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Now referring to FIG. 1, a schematic diagram of a preferred embodimentof the method and apparatus for surface treating animal tissue isprovided at reference numeral 10. It should be appreciated that whilethe invention is described in the context of surface treating animaltissue, the surface treatment is provided to reduce pathogenic bacterialpopulations on the surface of animal tissue if such bacterialpopulations are present. It is not necessary that a particular animaltissue which is processed according to the invention contains at least aminimal amount of pathogenic bacteria. It is expected that most animaltissue processed according to the invention will be essentially free ofpathogenic bacteria. In the context of processing animal tissue forhuman consumption, it is expected that there may be a possibility, atsome time, that pathogenic bacteria may exist on the surface of theanimal tissue. Accordingly, the present invention is provided to destroybacterial populations, if they exist, before the animal tissue isfurther processed or reaches the consumer.

It should be appreciated that the phrase “animal tissue” is meant todescribe relatively small portions of tissue obtained as a result of theslaughter and fabrication operation. In general, these small portionsinclude trimmings from animal carcasses. It is expected that the smallportions of animal tissue will have a size ranging from about 0.5 inchto about 16 inches in length. It should be understood that the length ofanimal trimmings refers to the longest dimension. In general, the animaltissue which can be processed according to the invention will generallyhave an average weight of between about 0.25 lbs and about 12 lbs. pertissue piece. Animal tissue can be obtained from several types of animalspecies including cattle, swine, sheep, poultry, horse, and wild game.It should be appreciated that the small portions of tissue do notinclude the entire carcass of large animals such as cattle and swine,but may include the entire carcass of poultry.

The apparatus for surface treating animal tissue 10, according to theinvention, includes a tissue inlet 12, a tissue outlet 14, and a surfacetreating or pasteurization unit 18. It should be appreciated that theinvention relates to the processing of animal tissue 16 to increase thedegree of certainty that pathogenic bacterial populations aresufficiently reduced or lowered thereby increasing the overall safety ofthe animal tissue as a food product, or as a pharmaceutical or animalfeed product.

The animal tissue 16 is continuously introduced into the pasteurizationunit 18 at the tissue inlet 12. The animal tissue 16 is provided by aconveyor 17 and dropped into the hot water 20 within the pasteurizationunit 18. The hot water is preferably provided at a temperature which issufficient to kill pathogenic bacterial populations which may be presenton the surface of the animal tissue 16 in the amount of time the tissueis provided within the pasteurization unit 18. In general, the hot watershould be provided at a temperature of between about 80° C. and about110° C. in order to provide desired lethal action on the bacterialpopulations which may be present on the surface of the animal tissue.

As the animal tissue 16 passes through the pasteurization unit 18, it isexpected that the animal tissue may pick up water during the heattreatment process. The heat treated tissue 22 is recovered from thepasteurization unit 18 and passes through a strainer 24 where the wateris allowed to drain therefrom. Preferably, the strainer 24 includes adrain screen 26 and a shaker 28. While the heat treated tissue 22 isprovided in the strainer 24, the agitation created by the shaker 28causes excess water to drain into a water catch pan 30 where it issubsequently removed via the water discharge line 54.

The heat treated tissue 22 which is recovered from the pasteurizationsystem 10 is then processed into edible products for human consumption.For example, the heat treated tissue 22 can be processed in a lowtemperature rendering process such as the process described by U.S. Pat.No. 5,725,897, the disclosure of which is incorporated herein byreference in its entirety. Alternatively, the heat treated tissue 22 canbe ground and processed into ground beef product as described, forexample, by Judge et al., Principles of Meat Science, 1989, pages135-174, and Price et al., The Science of Meat and Meat Products, 3dEdition, 1986, pages 431-457. Furthermore, the heat treated animaltissue 22 can be processed into other meat products or used forpharmaceuticals or animal feed.

The water temperature provided within the pasteurization unit 18 ispreferably provided within a range of between about 80° C. and about110° C. Applicants have discovered that by providing the water at atemperature within this range, and that by providing the animal tissue16 within the pasteurization unit 18 for between about 25 and about 50seconds, the desired degree of pasteurization of the surface of theanimal tissue 16 can be obtained. Hot water is fed to the pasteurizationunit 18 through the hot water inlet line 50. The flow of the hot waterthrough the inlet line 50 is controlled by the flow adjusting valve 52.Water is recovered from the pasteurization unit 18 via water dischargeline 54. Because the pasteurization unit 18 runs at steady state, theintroduction of a mass of water into the pasteurization unit causes theremoval of the same mass of water therefrom. Water can leave the systemas vapor and a certain amount of water is expected to be absorbed by theanimal tissue 16. The remaining amount of water flows out of thepasteurization unit along with the heat treated tissue 22 and isrecovered in the water catch pan 30. Water recovered in the water catchpan 30 then flows via water discharge line 54 into surge tank 56. Anadditional water recovery line 58 is provided. When the valve 60 isopen, water within the pasteurization unit 18 flows into the surge tank56. This allows for easy draining of the pasteurization unit 18 forcleaning.

The water which is introduced into the pasteurization unit 18 andrecovered therefrom can be referred to as processing water. While theembodiment of the invention depicted in FIG. 1 includes a recycle stream55 for the processing water, it should be appreciated that the inventioncan be practiced without the recycle stream. That is, processing waterfrom the pasteurization unit 18 can be discarded, and fresh heated watercan be introduced into the pasteurization unit 18. Furthermore, thesurge tank 56 is advantageous for allowing fat buildup in the processingwater to overflow. To assist the overflow of fat, water can be added vialine 57 at a rate controlled by the valve 59 to cause overflow of excessfat from the surge tank 56. In addition, the line 57 can be relied uponfor introducing water for making up the water which is evaporated orotherwise lost during the processing.

The processing water recovered in the surge tank 56 and the make upwater are processed and introduced into the pasteurization unit 18 forfurther processing of animal tissue 16. A valve 62 is provided whichcontrols the flow of water through the pump inlet line 64 and into therecirculation pump 66. Under pressure, water then passes through valve68 and pump outlet line 70 and then through the heat exchanger 72. Theheat exchanger 72 includes a steam inlet 74 and a condensation outlet 76for heating the water. Heated water 78 then flows out of the heatexchanger 72 for introduction into the pasteurization unit 18.

Now referring to FIGS. 2 and 3, the pasteurization unit 18 is shown indetail. The hot water is introduced into the pasteurization unit 18 viainjection ports 100. A greater number of injection ports 100 areprovided near the tissue inlet 12 in order to control the temperatureacross the length of the pasteurization unit. Because the animal tissue16 is provided at a much lower temperature than the water within thepasteurization unit 18, additional energy or heat should be providednear the inlet region. Along the length of the pasteurization unit 18, ascrew 104 is provided for advancing the animal tissue 16 along thelength of the pasteurization unit. The screw 104 includes a spiralflight 106. As the screw 104 rotates, the spiral flight 106 causes theanimal tissue 16 to move along the length of the pasteurization unit 18.This causes the animal tissue 16 to advance through the pasteurizationunit 18 on a first in first out basis thereby preventing overtreatmentof certain pieces of animal tissue 16. The speed of the screw 104 isadjusted to provide the desired residence time within the pasteurizationunit 18. It should be appreciated that the desired residence time is afunction of the temperature of the water within the pasteurization unit18. In the case of water provided at a temperature of between about 80°C. and about 110° C., it is desirable to provide a residence time ofbetween about 25 seconds and about 50 seconds, and more preferablybetween about 30 seconds and about 45 seconds. For a screw having asolid flight at a 12 inch pitch, this relates to a screw speed of 8-9revolutions per minute for a pasteurization unit having a length ofabout 10 feet. The screw 104 preferably driven by a variable speed motor108 which can be adjusted to provide the desired tissue retention timewithin the pasteurization unit 18.

At the outlet end of the pasteurization unit 18, the final edge of theflight pushes the animal tissue above the water level and out onto thestrainer 24. The water is then recovered and recirculated into thepasteurization unit 18. The heat treated tissue 22 is then recovered andfurther processed by, for example, those techniques previouslydescribed.

It should be appreciated that the purpose of the pasteurization unit isto provide a relatively fast heat treatment of the animal tissue inorder to reduce the incidence of pathogenic bacteria while retaining thedesired organoleptic properties of the animal tissue. In particular, itis desirable to provide at least one log reduction in the aerobic platecounts on the surface of the animal tissue, and to provide at least atwo log reduction in pathogenic bacteria when tested using inoculatedsamples. It is expected that the animal tissue will pick up a certainamount of water as a result of the processing. It is desired, however,that this increase in weight is minimal.

It should be appreciated that the invention provides for the surfacetreatment of the animal tissue. It is not desirable to treat the animaltissue to a depth below about 4 mm from the surface of the animaltissue. It is expected that if surface treatment extends beyond about 4mm, the organoleptic properties of the animal tissue will becompromised.

An alternative way of characterizing the surface treatment of animaltissue within the pasteurization unit is in terms of the ratio of theflow rate of heated water into the pasteurization unit to the flow rateof animal tissue into the pasteurization unit. In order to providedesired degree of surface treatment of the animal tissue, enough heatenergy needs to be introduced into the pasteurization unit. Too muchheat energy, however, will result in cooking the animal tissue ordeterioration of organoleptic properties of the animal tissue. It shouldbe appreciated that the desired flow ratio of water to animal tissue isa function of the temperature of the water bath within thepasteurization unit, the length of time the animal tissue will remainwithin the pasteurization unit, and the temperature of the animal tissueupon entry into the pasteurization unit. In the case of poultry, theanimal tissue is often processed relatively shortly after the slaughteroperation. Accordingly, the temperature of poultry which has beenrecently slaughtered and after removal of the feathers is between about30° C. and about 40° C. In contrast, beef trimmings are generally cooledor chilled to a temperature of between about 0° C. and about 10° C.prior to introduction into the pasteurization unit. It should beappreciated that a higher flow rate of water may be appropriate for alower temperature animal tissue. In contrast, a lower flow rate of watermay be appropriate for a hotter temperature animal tissue. Furthermore,the flow rate of water will be affected by the temperature of the waterintroduced into the pasteurization unit and the temperature of the watermaintained within the pasteurization unit. In general, under conditionsof providing a bath at between about 80° C. and about 110° C. andintroducing animal tissue at a temperature of between about 0° C. andabout 40° C., it is desirable to provide a flow rate ratio of water toanimal tissue of between about 0.05 gallon of water per pound animaltissue to about 0.2 gallon of water per pound animal tissue. Preferably,the flow ratio is between about 0.10 gallon of water per pound animaltissue and about 0.15 gallon of water per pound of animal tissue.Applicants have found that a most preferred flow ratio is between about0.11 gallon of water per pound of animal tissue and about 0.13 gallon ofwater per pound of animal tissue.

By way of illustration, the pasteurization unit can be used to process14,000 pounds of animal tissue per hour and provided at a temperature ofbetween about 0° C. and about 10° C. by introducing 1700 gallons ofwater provided at a temperature of between about 80° C. and about 110°C. It is expected that with such a flow rate of water, about 1550gallons per hour will be provided as recirculated water, and about 150gallons per hour will be provided as make-up water. Surface treatingabout 10,000 pounds per hour provided at a temperature of between about0° C. and about 10° C. can include introducing about 1100 gallons ofwater per hour provided at a temperature of between about 80° C. andabout 110° C. Of that amount, about 1000 gallons can be recirculatedwater and about 100 gallons can be make-up water.

While a preferred embodiment of the invention is described in thecontext of hot water as a heating media, it should be appreciated thatother types of heating media can be used according to the invention. Ingeneral, it is preferable to use a heating media which providessufficiently fast heat transfer to the surface of the animal tissue. Theheating media can be referred to as the bath. The heat transfercoefficient of a media reflects the relative ability of the media totransfer its heat energy to another substance. The heat transfercoefficient of boiling water is significantly higher than convectiveoil. The average heat transfer coefficient for boiling water is 20 timesgreater than for convective oil. In the situation where tallow is usedas the heating media and where it is provided at a temperature in therange of between about 80° C. and 110° C., it may be appropriate tosurface treat animal tissue for between about 25 seconds and 150seconds. Because the heat transfer coefficient of tallow is less thanthe heat transfer coefficient of water, it may be appropriate toalternatively increase the temperature of the tallow to provide thedesired lethal effect under treatment times similar to that used whenwater is the heating media. For example, tallow can be provided at atemperature of less than about 150° C. if it is desirable to providesurface treatment of the animal tissue for less than 150 seconds. Whenthe tallow is provided at such a higher temperature, it may be desirableto reduce the treatment time to between about 25 seconds and about 50seconds.

The pasteurization technique of the invention is useful for processingbeef trimmings for ground beef manufacture, offal, and variety meats.The pasteurization technique of the invention is particularly useful forlow temperature rendering applications because of the potential risksassociated with heating raw meat products from 4° C. to 42° C. and thepotential growth of pathogenic bacteria at these sub-lethaltemperatures. Low temperature rendered products (Finely Textured Beefand Partially Defatted Chopped Beef) are primarily used as components ofground beef, beef pattie, and further processed meat products. Theaddition of a pasteurization step prior to the low temperature renderingprocess would lower the risk of pathogenic bacteria entering the system.

EXAMPLE 1 Time-temperature Lethality Study

Product Treatment

A Blentech ContinuTherm™ continuous thermal screw was used having ascrew conveyor immersed in a heating media. The heating media used inthe testing was either hot water or hot tallow. The treatment time iscontrolled by the rotational speed of the screw conveyor. The treatmenttimes used in this study were 30, 45, or 90 seconds. The products testedwere fresh beef trimmings containing 90%, 50%, or 30% lean. Thefollowing product-time-media combinations were tested:

Product Time, seconds Media 90% lean 30, 45, and 90 Hot Water 50% lean30, 45, and 90 Hot Tallow 30% lean 30, 45, and 90 Hot Tallow

Microbiological Analysis

The products were sampled before and after treatment to determine thereduction effect of the time-treatment combination. The products weresampled by randomly selecting approximately 1200 g of product andgrinding (3 mm plate) twice through a small meat grinder, which had beenheat sterilized. The sample was then aseptically mixed and a 20 g samplewas removed. This sample was placed in a stomacher bag into which 180mls of sterile 0.1% peptone water was added. The sample was thenhomogenized in a stomacher for 60 seconds. The samples were thenserially diluted and plated on Petrifilm™ according to themanufacturer's recommendations (3M, 1997). Aerobic Plate Count,Coliform, and E. coli (Biotype I). All results were expressed andanalyzed as log CFU/cm². The lowest detection limit of this test was 1log CFU/g.

Data Analysis

Before and After treatment data were analyzed using a paired t-test(P<0.01) to determine if the treatment resulted in a significantreduction. Significant treatment time differences, within product-mediacombinations, were determined using least significant differencescomparisons (P<0.01).

Two heating medias (water and oil) in combination with three treatmenttimes (30, 45, and 90 seconds) were studied. Table 1 shows the AerobicPlate Count reductions. All treatments showed significant Aerobic PlateCount reductions (P<0.05). Since different products were tested for eachheating media, comparisons were not made between media types. Increasedtreatment time did not increase lethality within media-productcombinations except for the hot tallow-30% lean combination. TheColiform and E. coli counts were too low to analyze for reductions.Table 2 shows the percent of samples with detectable Coliform and E.coli.

TABLE 1 Aerobic Plate Count Reductions Pro- duct, Trt Before After %Time, Treatment, Treatment, Reduction, N lean Media seconds log CFU/cm²log CFU/cm² log CFU/cm² 12 90% Water 30 5.23 2.91 2.32 6 90% Water 455.56 2.65 2.91 6 90% Water 90 6.12 3.32 2.8 14 50% Tallow 30 3.72 2.760.96 8 50% Tallow 45 3.11 2.08 1.03 6 50% Tallow 90 4.1 3.21 0.88 14 30%Tallow 30 7.19 5.79 1.39 8 30% Tallow 45 8.08 6.69 1.39 6 30% Tallow 906.2 4 2.2 E. coli Trt Coliform (Biotype I) Product, Time, Before,Before, After, N % lean Media seconds % After, % % % 12 90% Water 30 7517 92 33 6 90% Water 45 100 0 100 0 6 90% Water 90 67 17 100 33 14 50%Tallow 30 36 14 0 0 8 50% Tallow 45 100 0 0 0 6 50% Tallow 90 12.5 0 0 014 30% Tallow 30 43 43 7 0 8 30% Tallow 45 12.5 0 0 0 6 30% Tallow 90100 0 0 0 *All reductions were significant (P <.05)

EXAMPLE 2 Water Absorption Study

Product Treatment

Fresh beef trimmings (90% lean and 50% lean) were cut and assigned toone of three treatment groups based on piece size (5 cm³, 10 cm² by 7.6cm, or 15 cm² by 7.6 cm). The pieces were then weighed, treated inboiling water for 30 seconds, and weighed after treatment. The scaleaccuracy was +/−1.5 grams. Samples were gently turned to allow excessfree water to drain from the sample. No vigorous action was used to freewater.

Data Analysis

Data were analyzed using least significant differences multiplecomparison to determine significant differences between treatments.Simple correlation analysis was used to determine if any relationshipsexisted between initial piece weight and water absorption.

Water absorption was not correlated to piece size. No significantdifferences were detected between lean type or piece size. The samplesin this test were gently turned to allow free water to drain. Wespeculate that aggressive shaking would result in lower waterabsorption. The data is shown in Table 3.

TABLE 3 Percent Water Absorption in Fresh Beef Trimmings Treated in HotWater Aver- Piece Size n 90 Lean Beef Trim 50 Lean Beef Trim age 5 cm³16 0.88 1.2 1.04 10 cm² × 7.6 cm 16 0.17 0.82 0.5 15 cm² × 7.6 cm 10(0.11) 3.24 1.57 Average 0.37 1.53 0.95

EXAMPLE 3 Pathogen Challenge Study

Product Treatment

This study utilized beef lean (Cutaneous truncii) and adipose tissue(subcutaneous tissue covering the Longissimus dorsi). These samples werecut to approximately 20 cm by 20 cm then inoculated with a mixture ofSalmonella typhimurium, Escherichia coli 0157:H7, and Listeriamonocytogenes. Three replicates of each treatment were performed on eachof three days (n=9). However, due to a lab error the E. coli 0157:H7culture was omitted during two of the days resulting in n=9 for S.typhimurium and L. monocytogenes, and n=3 for E. coli 0157:H7. The leanand adipose samples were randomly assigned to each of two treatments.This resulted in four treatment-tissue combinations (Water-Lean, WaterAdipose, Tallow-Lean, and Tallow-Adipose). Immediately prior totreatment four cores (11.4 cm² each) were removed for microbial analysis(BEFORE).

For the water treatment individual samples were immersed for 30 secondsin boiling water (approximately 98° C.). During the treatment the watertemperature decreased to approximately 96° C. as energy was absorbed bythe sample. The water treatment apparatus consisted of an eight literstainless steel container with approximately five liters of tap waterplaced on a laboratory hot plate. Immediately following treatment fourcores (11.4 cm² each) were removed (AFTER).

The tallow treatment involved immersing individual samples in hot beeftallow (121° C.) for 45 seconds. The apparatus consisted of a stainlesssteel eight liter container filled with approximately five liters ofbeef tallow. This container was placed in a heated bath of corn oil. Thecorn oil was maintained at the desired temperature (121° C.) and used toheat the tallow. During treatment the tallow temperature dropped toapproximately 118° C.

Microbiological Analysis

Culture Preparation

Stock cultures of Listeria monocytogenes Scott A, Escherichia. coli0157:H7 (rifampicin resistant) and Salmonella typhimurium (naladixicacid resistant) were transferred to tryptic soy broth or tryptic soybroth with 0.6% yeast extract (L. monocytogenes) and incubated overnightat 37° C. 0.5 ml portions of each of the overnight cultures weretransferred to individual flasks containing 33.5 mls of tryptic soybroth (with yeast extract for L. monocytogenes) and incubated in agyro-rotary shaker incubator at 37° C. for 24 hours at 115 rpm. Theovernight cultures were then combined in 1000 mls of sterile distilledwater to produce the mixed inoculum for the tissue.

Tissue Inoculation

Lean and adipose tissues were inoculated by immersion for 5 minutes,turning each of the pieces over at 2.5 minutes. The inoculated sampleswere allowed to drain approximately 2 minutes, then covered and wereheld refrigerated (5° C.) for approximately 18 hours to allow forattachment of the microorganisms. The target inoculation level was 5log.

Sampling

Prior to treatment (BEFORE) and after treatment (AFTER), each tissue wassampled by removing 2 cores from diagonal corners. The cores wereaseptically excised all of the way through each tissue piece, such thateach core consisted of two external inoculated surfaces. The area ofeach surface was 11.4 cm², so that each core represented 22.8 cm² ofsurface. The two cores were composited into a single sample, such thatthe composite sample represented 45.6 cm².

Bacterial Enumeration

The composite samples were homogenized in sterile, buffered 0.1% peptonewater for 2 minutes in a stomacher. The samples were serially diluted inbuffered peptone water, and then spiral plated using either a Model D orAutoPlate 3000. Bacterial populations were enumerated using tryptic soyagar (Aerobic Plate Count), XLD agar containing 200 ppm naladixic acid(Salmonella), Listeria selective agar (modified Oxford formulation;Listeria) and Sorbitol MacConkey Agar containing 200 ppm rifampicin (E.coli 0157:H7). The plates were incubated at 37° C. for 24-48 hours, andthe estimates of the bacterial populations converted to log colonyforming units per cm² (log CFU/cm²). Bacterial reductions werecalculated by subtracting the AFTER results from the BEFORE results.Percent pathogen reduction was calculated from the integer value.

Data Analysis

Before and After treatment data were analyzed using a paired t-test(P<0.01) to determine if the treatment resulted in a significantreduction. Treatment differences were analyzed for using a one-wayANOVA.

Both the hot water and the hot tallow treatments were successful inreducing the pathogenic bacteria in this test. All treatments showedsignificant reductions of all pathogens tested. Water had asignificantly higher lethality for Listeria monocytogenes than tallow.Tables 4, 5, and 6 show the results from these treatments.

TABLE 4 Salmonella typhimurium Reduction Using Pasteurization ProcessBefore After Reduction, Reduc- Treatment, log Treatment, log log tion,Treatment CFU/cm² CFU/cm² CFU/cm² % Water-Lean 4.81 3.47 1.34 95.4Water-Adipose 5.93 3.04 2.9 99.9 Tallow-Lean 5.91 4.44 1.47 96.6Tallow-Adipose 5.73 4.38 1.35 95.5 Nine replicates Water treatment-98°C., 30 seconds Tallow treatment-121° C., 45 seconds

TABLE 5 Listeria monocytogenes Reduction Using Pasteurization ProcessBefore After Reduction, Reduc- Treatment, log Treatment, log log tion,Treatment CFU/cm² CFU/cm² CFU/cm² % Water-Lean 6.37 4.18 2.19 99.4Water-Adipose 6.61 4.48 2.13 99.3 Tallow-Lean 6.38 5.33 1.05 91.1Tallow-Adipose 6.67 5.71 0.96 89 Nine replicates Water treatment-98° C.,30 seconds Tallow treatment-121° C., 45 seconds

TABLE 6 Escherichia coli 0157:H7 Reduction Using Pasteurization ProcessBefore After Reduction, Reduc- Treatment, log Treatment, log log tion,Treatment CFU/cm² CFU/cm² CFU/cm² % Water-Lean 4.68 2.74 1.94 98.9Water-Adipose 4.64 2.64 2 99 Tallow-Lean 5.39 3.93 1.46 96.5Tallow-Adipose 4.34 3.3 1.04 90.9 Nine replicates Water treatment-98°C., 30 seconds Tallow treatment-121° C., 45 seconds

Both hot water and hot tallow treatment showed significant reductions inAerobic Plate Count, Salmonella typhimurium, Listeria monocytogenes, andEscherichia coli 0157:H7.

Increasing treatment times did not significantly improve APC reductions,therefore 98° C. for 30 seconds was chosen as the treatment for the hotwater pathogen study. Equipment limitations required that the tallowtemperature be reduced to 121° C. The tallow pathogen study wasconducted at 121° C. for 45 seconds.

Hot water treatment caused minimal water absorption. This waterabsorption can be reduced by mechanical action.

Hot water treatment consistently resulted in higher pathogen lethality.The increased lethality was attributed to a much higher heat transfercoefficient for boiling water. Hot water treatment is also more energyefficient and is much easier to handle than tallow (data not shown).

We claim:
 1. A method for surface treating animal tissue, the methodcomprising steps of: (a) introducing beef trimmings from a fabricationoperation and having an average size of between about 0.5 inch and about16 inches in length into a water bath provided at a temperature ofbetween about 80° C. and about 110° C. for between about 25 seconds andabout 50 seconds; (b) conveying the beef trimmings through the waterbath in a first in and first out arrangement by turning a rotationscrew; (c) recovering the beef trimmings from the water bath; and (d)collecting processing water from the water bath, separating fat from theprocessing water by phase separation, and returning the processing waterto the water bath.
 2. A method for surface treating animal tissueaccording to claim 1, wherein the step of conveying the beef trimmingsthrough the water bath comprises turning a rotation screw having aspiral flight extending through the water bath for advancing the beeftrimmings.
 3. A method for surface treating animal tissue according toclaim 2 comprising rotating the rotation screw at a rate of between 1revolution per minute and 20 revolutions per minute.
 4. A methodaccording to claim 1, further comprising a step of: (a) processing therecovered beef trimmings to provide ground beef.
 5. A method accordingto claim 1, wherein the beef trimmings are provided at a temperature ofbetween about 0° C. and about 10° C. before being introduced into thewater bath.
 6. A method for surface treating animal tissue according toclaim 1, wherein the beef trimmings have an average size of betweenabout 0.25 lb. and about 12 lbs.
 7. A method for surface treating animaltissue, the method comprising steps of: (a) introducing beef trimmingsfrom a fabrication operation and having an average size of between about0.25 lb. and about 12 lbs. per piece of beef trimmings into a water bathprovided at a temperature of between about 80° C. and about 110° C. forbetween about 25 seconds and about 50 seconds; (b) conveying the beeftrimmings through the water bath in a first in and first out arrangementby turning a rotation screw; (c) recovering the beef trimmings from thewater bath; and (d) removing processing water from the water bath,separating fat from the processing water by phase separation, andreturning the processing water to the water bath.
 8. A method forsurface treating animal tissue according to claim 7, wherein the step ofconveying the beef trimmings through the water bath comprises turning arotation screw having a spiral flight extending through the water bathfor advancing the beef trimmings.
 9. A method for surface treatinganimal tissue according to claim 8 comprising rotating the rotationscrew at a rate of between 1 revolution per minute and 20 revolutionsper minute.
 10. A method according to claim 7, further comprising a stepof: (a) processing the recovered beef trimmings to provide ground beef.11. A method according to claim 7, wherein the beef trimmings areprovided at a temperature of between about 0° C. and about 10° C. beforebeing introduced into the water bath.
 12. A method for surface treatinganimal tissue, the method comprising steps of: (a) introducing beeftrimmings from a fabrication operation and having an average size ofbetween about 0.5 inch and about 16 inches in length into a water bathprovided at a temperature of between about 80° C. and about 110° C. forbetween about 25 seconds and about 50 seconds; (b) conveying the beeftrimmings through the water bath in a first in and first outarrangement, the animal tissue being conveyed through the water bath byturning a rotation screw having a spiral flight for advancing the beeftrimmings through the water bath, wherein the rotation screw is rotatedat a rate of between about 1 revolution per minute and about 20revolutions per minute; and (d) recovering the beef trimmings from thewater bath.
 13. A method according to claim 12, wherein the beeftrimmings are provided at a temperature of between about 0° C. and about10° C. before being introduced into the water bath.
 14. A methodaccording to claim 12, further comprising a step of: (a) processing therecovered beef trimmings to provide ground beef.
 15. A method accordingto claim 12, wherein the beef trimmings have an average size of betweenabout 0.25 lb. and about 12 lbs.